Well if you ask gort (which I wouldn't ) it might be a good thing, but if you ask most people it's not.

The reason that dead space is not a good thing is that it is empty space that the compressed air coming from you chamber has to fill before it can start to force your projectile out the barrel, there by reducing the pressure and volume of air that is available to fire the projectile.

A valve on the bottom is also easier to use for multiple guns if you must, since I haven't bound another sprinkler valve yet I use the same one on by big pneumatic as on my PB pneumatic and every time I have to change it I have to take out my 1/4" nipple and blow gun so it can clear the chamber since they run parallel...

But if you have the pipe coming out of the chamber long and the pipe after the 2 elbows short, the valve will be behind the chamber so it wont matter...

<img src="http://img170.imageshack.us/img170/6743/setuptypespn7.png">

On the top one you have to remove the blowgun or the hose barbs to get the valve off easily...

But the top one can be used if you make the pipe in between the 2 elbows LONG, but that just looks stupid...